1. Field of the Invention
This invention relates to error detection in nonbinary correlative systems, and more particularly to error detection for a 7-level correlative signal.
2. Description of the Prior Art
The method of generating, recovering and detecting errors in multilevel nonbinary systems has been disclosed in my invention which issued as U.S. Pat. No. 3,601,702. It was there noted that the correlation properties of the transmitted wave can be used to detect errors and thus obviate the need of introducing redundant digits into the input binary data. Logic and sampling circuits provide a replica of the binary input data in parallel form except for errors that might have occurred in the transmission of the waveform. This binary data is coded in exactly the same way as in the transmitter. The principle is to ascertain which of the extreme levels, i.e., top and bottom levels, correspond to the present and past digits emanating from the decoder and digital memory. A comparison is made at the sampling instant of the digit. If there is a disagreement, an error is indicated and the memory is reset to the correct state. Such a comparison is done when the extreme levels are present because only the extreme levels are formed in a unique way in the correlative systems. Intermediate levels may be formed in more than one way and therefore are not suitable for the detection of errors. A similar result is achieved by the present invention but this is accomplished by means of novel logic arrangements as will be described hereinbelow.